PORTLAND    CEMENT    MATERIALS    NEAR   DUBUQUE,  IOWA.        231 
maximum  allowable  limits  of  5  to  6  per  cent.  Certain  of  the  lime- 
stone beds  that  are  high  in  silica  resemble  very  closely  in  composi- 
tion the  " cement  rock"  of  the  well-known  Lehigh  Portland  cement 
district. 
The  materials  in  this  district  would  require  very  little  preliminary 
ilrying.     The  limestone  is  fairly  uniform  in  texture,  but  it  would  need 
^ery  thorough  grinding.     The  shale,  clay,  and  loess  are  less  refractory, 
and  although  the  clay  and  loess  carry  a  few  chert  or  quartz  pebbles 
uch  objectionable  material  is  not  excessive  and  could  be  removed 
y  screening. 
The  Dubuque  district  is,  of  course,  not  ideally  situated  with  regard 
to  a  fuel  supply,  but  its  distance  from  the  Iowa  coal  field  is  not  so 
great  as  the  distance  of  certain  successfully  operated  cement  plants 
Prom  their  fuel  base.  A  possible  substitute,  at  least  in  part,  for  coal 
might  be  furnished  by  the  great  quantities  of  sawdust  and  slabs 
wasted  by  the  several  sash  and  door  factories  and  other  lumber  mills 
at  Dubuque.  This  fuel  might  be  utilized  in  the  kilns  in  the  form  of 
producer  gas. 
